Intended for healthcare professionals

Clinical Review Science, medicine, and the future

Behaviour and genes

BMJ 1999; 319 doi: (Published 03 July 1999) Cite this as: BMJ 1999;319:37
  1. Peter McGuffin, director (,
  2. Neilson Martin, MRC PhD studentb
  1. a Social Genetic and Developmental Psychiatry Research Centre, Institute of Psychiatry, Kings College London, London SE5 8AF
  2. b Division of Psychological Medicine, University of Wales College of Medicine, Cardiff CF4 4XN
  1. Correspondence to: P McGuffin

    New discoveries in genetics seem to hit the headlines almost daily, and probably the most eyecatching and controversial are those dealing with human behaviour. Thus, there has been popular media interest in reports of genes conferring susceptibility to psychiatric diseases and a whole range of “genes for” traits such as aggression, intelligence, and neuroticism. The scope for sensationalism and oversimplification is great. Here, we outline some of the basic concepts and lines of evidence from quantitative genetics indicating that genes do have important influences in determining human behaviour but that this nearly always involves an interplay with the environment. We then look at ways in which molecular methods are being used to locate and identify genes and how such approaches may impact on clinical practice.

    Behaviour runs in families

    We tend to resemble our parents, siblings, and other close relatives not just in the way we look but in the way we behave. However, the types, patterns, and causes of familial behavioural traits are extremely varied. They range from rare single gene disorders, such as Huntington's disease, that present with dramatic changes in behaviour in adult life, to commoner but more genetically complex disorders, such as schizophrenia and manic depression, through to normal variation in traits that are usually measured quantitatively, such as personality or intelligence.1 They can also include characteristics such as political or religious persuasion and career choice.

    One of the basic pitfalls in studying the genetics of behaviour (or indeed any other type of trait) is to assume that familiality necessarily implies genetic transmission or that strong evidence of familial clustering implies single gene effects. Geneticists have long been aware that mendelian inheritance can be simulated by other mechanisms.2 To illustrate this, McGuffin and Huckle studied the educational histories of the families of a cohort of medical students: they …

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